CN201429406Y - Two-wire current mode displacement sensor - Google Patents

Abstract

The utility model discloses a two-wire current mode displacement sensor, comprising an eddy current inductive probe formed by a TLP355 integrated circuit and an inductance core, a voltage doubling rectification circuit, a voltage emitter follower, a current divider, an XTR115 integrated circuit and an interference suppressor circuit both special for converting voltage or current. The standard two-wire electric current loop output can realize dynamic test by changing the size of the probe, extending linear behavior, and correcting linearity and the like as required. The circuits can be of the smallest sizes within an allowed range of the circuit size. The two-wire current mode displacement sensor has the advantages of high linearity degree, strong consistency, small temperature drift, strong disturbance-resisting capacity, simple circuits, simple production debugging and correction and the like.

Description

Two-wire system current mode displacement transducer

Technical field

The utility model relates to the non-contact detecting sensor to the metal displacement, relates in particular to a kind of sensor that is used for the tension force non-contact detecting.

Background technology

At present, the tension force non-contact detecting has advantages such as not having machinery wearing and tearing, long service life.Though conductive plastic potentiometer precision height, good linearity need be rigidly connected, and mechanical wear directly influences serviceable life, and the conductive plastic potentiometer of quality better is expensive.

In order to address these problems, the non-contacting metal displacement transducer that uses is as JCW displacement transducer series at present, use discrete component and LC oscillator to form eddy current sensor, then the change in electric of inductance value is carried out processing and amplifying, again the mode of exporting with the amplifier switching current.Shortcoming is exactly poor linearity, and is dynamically little, and it is big surely to float coefficient, and consistance is low, and the electric current loop load capacity of amplifier conversion is also poor.Power supply needs configuration in addition, supply circuit after the voltage stabilizing, and the circuitry consumes electric current is big, greater than 4mA, can't use the form of two-wire system electric current loop output, gearing uses frequency converter in a large number at present, the electric current loop input interface that standard is all arranged, very inconvenient on such sensor uses; Also very complicated in producing debugging, proofreading and correct in addition, unfavorable mass, the pattern of low-cost production.

In order to overcome these problems, the amplifier of back level tie processing is also arranged, request for utilization is to have satisfied, cost has also got on naturally.Also have external product to adopt the product of the lsi development of special designs, its price is very high, can't satisfy low price, high performance tension force non-contact detecting occasion.

Summary of the invention

The utility model is the shortcoming that exists at prior art, adopt special-purpose high performance integrated circuit at a low price to form the LC oscillator, the special-purpose current conversion integrated circuit of current conversion, the electric current loop of standardization two-wire system is exported, and detection dynamically can be realized by changing modes such as probe size, expansion linear dynamic, correction linearity as required.Under circuit volume permission situation minimum on the volume, realize minimizing.And want linearity height, consistance is strong, temperature float little, the antijamming capability height; Circuit is simple, produces debugging and proofreaies and correct simply, is fit to mass production.

The utility model is realized by the following technical solutions:

The utility model constitutes the vortex induction probe by TLP355 integrated circuit and inductance core, and ac rectifier, voltage are penetrated a grade follower, shunt, and XTR115 voltage/current conversion special IC, anti-jamming circuit are formed.The accurate voltage stabilizer voltage of described XTR115 voltage/current conversion special IC is supplied with the TLP355 integrated circuit, TLP355 integrated circuit and inductance core constitute the vortex induction probe, extract oscillator signal at the inductance two ends and carry out voltage multiplying rectifier, amplifier is penetrated level and is followed the back shunting to XTR115 voltage/current conversion special IC, the electric current 4-20mA that converts to output.

The periphery of described magnetic core, non-sensitive surface coated metal thin layer, and weld an electric capacity and link to each other with power cathode.

Described XTR115 voltage/current conversion special IC is imported the magnetic bead of connecting in the electric power loop, TVS in parallel pipe.

Described vortex induction probe is the TLP355 integrated circuit, FERRITE CORE and coil and oscillating capacitance are formed, the inductance low-power consumption, inside has constant current source, this integrated circuit originally is the special circuit near switch, belong to the non-failure of oscillation type of amplitude change type special circuit, the wide 4.5-36V direct current of its operating voltage, static working current is less than 0.5mA.The utility model only is used for the LC oscillator to this integrated circuit, and the LC coil excitation is according to electromagnetic induction principle, when sheet metal during near the coil winding of an alternating magnetic field, sheet metal is equivalent to the coil winding of a short circuit, produces the induction ring current, is called eddy current.The angular frequency of the resistivity of its size and sheet metal, magnetic permeability, thickness, coil excitation electric current and the relating to parameters such as distance between sheet metal.When the coil winding of short circuit can produce sizable electric current, the magnetic flux of the coil winding of its magnetic flux and alternating magnetic field subtracts each other, and the coil winding magnetic flux of alternating magnetic field descends and impels self electric current to increase.Sheet metal is the closer to the coil winding of alternating magnetic field, and the coil winding electric current of alternating magnetic field is big more, and the eddy current that produces on sheet metal is also big.Because kelvin effect produces eddy current and reacts on the coil in the thin layer of metal surface, make and produce induced potential in the coil, causes the variation of coil equiva lent impedance thus, thereby also causes the variation of oscillating voltage amplitude.Based on this principle, its feature: when metallic object during near the probe of TPL355 integrated circuit and LC coil core composition, the diameter size of its inductance core is in the 5-100mm scope, the voltage drive amplitude at coil two ends descends, and its amplitude is the funtcional relationship that the metallic object and the displacement of probe become substantially linear.

In order to satisfy the tonometry of various occasions, the displacement that needs different ranges, the probe size of the coil of change LC and the composition of magnetic core, the distance of the probe of the coil among metallic object and the LC and the composition of magnetic core change the voltage magnitude and the proportional variation of distance at coil two ends.

Characteristic according to TLP355 integrated circuit itself, adjust feedback resistance and can revise the oscillating voltage amplitude, therefore if because inductance in the probe of the composition of the coil of LC and magnetic core and electric capacity and magnetic core magnetic flux thereof when deviation is arranged, its feature: can adjust this feedback resistance the voltage magnitude of coil is met the demands.

The signal that the vortex induction probe is gone up the coil two ends is a sine wave signal, amplitude is the funtcional relationship of the displacement twenty percent substantially linear of metallic object and probe, need become the DC simulation voltage signal to this conversion of signals,, adopt the voltage multiplying rectifier increase rate because signal amplitude is smaller.DC simulation voltage signal amplitude after the rectification; Its feature: the slight distortion of high-end and the low side linearity, technical requirement according to inductance core, the reliable detection distance is at below 60% of core diameter, therefore non-cpntact measurement need be reserved certain non-contacting free mechanical trip at lower position, and getting high-end and the linearity low side interlude is that the dynamic range data are more satisfactory.

The oscillating voltage amplitude feedback resistance size of TLP355 integrated circuit is relevant with the inductance value of coil, when being used for regulating at nonlinear area near the switch use, regulating its feature in this use to cooperate the range of linearity of its low side of coil on vortex induction probe: feedback resistance only needs 10% resistance to satisfy inductance and electric capacity and the correction devious of magnetic core magnetic flux thereof in the probe of composition of the coil of LC and magnetic core.

DC simulation voltage behind the voltage multiplying rectifier is formed electric current by amplifier again and is penetrated a grade follower, for subordinate's voltage divider and voltage/current conversion, provides impedance matching.Its feature: DC simulation voltage input amplifier, amplifier is formed voltage and is penetrated a grade follower, and output voltage is followed input voltage, and the maintenance amplitude is constant, improves driving force, the supply voltage of amplifier.

The shunt effect is split into step voltage/electric current needed range of current in back to the voltage of penetrating grade follower, and shunt has adopted potentiometer to shunt.Its feature: shunt is regulated the electric current of DC simulation voltage maximum, makes this electric current satisfy the input requirement of back level change-over circuit, also is simultaneously the higher limit of regulating the displacement dynamic range.

The XTR115 integrated circuit belongs to the two-wire system current transducer, and inner 2.5V reference voltage can be used as the driving source of sensor.40～200 μ A weak current signals that XTR115 can produce sensor amplify 100 times, obtain the standard output of 4～20mA.When loop current can automatic current limiting during near 32mA.

1) increased in the chip+the accurate voltage stabilizer of 5V, its output voltage precision is ± 0.05%, and voltage temperature coefficient only is 20 * 10-6/ ℃, powers for external circuit separately, thereby has simplified the design of external power source.

2) precision height, nonlinearity erron is little.Conversion accuracy can reach ± and 0.05%, nonlinearity erron only is ± 0.003%.

3) allowed band of loop power voltage is wide, Us=7.5～36V.XTR115 is powered by loop power.

The utility model adopts its technical characterstic of XTR115, and the loop power power supply provides+characteristics of the accurate voltage stabilizing of 5V, and the electric current of prime can be amplified the standard output that convert 4～20mA to; Its feature: two-wire system electric current loop loop, provide+the accurate voltage stabilizing of 5V penetrates the power supply of grade follower to TPL355 integrated circuit and electric current, becomes the current amplifying process of shunt the normalized current in two-wire system 4～20mA of standard to export simultaneously.

The quiescent dissipation that TLP355 integrated circuit and voltage are penetrated grade follower is very little, and DC simulation voltage linear lower limit is also low, and XTR115 conversion back minimum voltage can not guarantee to reach 4mA, just need use the measure of current boost to whole loop.To the 2.5V reference voltage or+5V is to XTR115 tripod resistance in parallel, adjusts to make output equal 4mA, this measure does not influence conversion.

TLP355 integrated circuit and inductance core constitute the vortex induction probe and belong to the higher-order of oscillation, under the present with serious pollution situation of space electromagnetic wave, need take a kind of measure to reduce the interference of electromagnetic wave to the higher-order of oscillation, concrete mode magnetic core is wrapped back electric capacity of welding with the whole circle of sheet brass and is connected with power cathode; Raising is disturbed from the power supply of power line, uses high-power frequency conversion equipment general now, and the interference of power line is very serious, and electric power loop is at the input end magnetic bead of connecting, both ends of power TVS pipe in parallel, and the electric current loop wire uses the braid shielded line.

For the expansion of linear dynamic, except that the size that changes probe, metallic object is done tangent motion to the induction part of sensor, does different in nature sector according to linear characteristics and detects and eccentric mode extended dynamic.

The beneficial effects of the utility model are: circuit adopts ready-made ripe integrated circuit at a low price, the ingenious performance wherein of having used, make the circuit of two-wire system current mode displacement transducer succinct, change detection and dynamically can realize by change probe size, expansion linear dynamic, correction linear mode as required; Linearity height, high conformity, temperature are floated little, and antijamming capability is strong; Circuit is simple, produces debugging and proofreaies and correct simply, changes the size of probe, just can produce the displacement transducer of different ranges, is fit to mass production.

Description of drawings

Fig. 1 is the utility model electromagnetic induction principle synoptic diagram;

Fig. 2 is the utility model electromagnetic induction schematic equivalent circuit;

Fig. 3 is the utility model electrical principle synoptic diagram;

Fig. 4 is the utility model linear graph;

Fig. 5 is the utility model inductance core structural representation;

Fig. 6 is the utility model probe shield synoptic diagram;

The number in the figure explanation

The coil rack 4-jar type magnetic core that the skeleton 3-coiling of 1-jar type magnetic core 2-coil is good

5-TLP355 integrated circuit 6-XTR115 integrated circuit 7-voltage is penetrated a grade follower 8-thin metal layer

9-sensitive surface 10-plastic casing 11-epoxy resin

Embodiment

Below in conjunction with specific embodiment, further specify the utility model and how to realize:

Embodiment

According to electromagnetic induction principle, when sheet metal during near the coil winding of an alternating magnetic field, sheet metal is equivalent to the coil winding of a short circuit, produces the induction ring current, is called eddy current.The angular frequency of the resistivity of its size and sheet metal, magnetic permeability, thickness, coil excitation electric current and the relating to parameters such as distance between sheet metal.When the coil winding of short circuit can produce sizable electric current, the magnetic flux of the coil winding of its magnetic flux and alternating magnetic field subtracts each other, and the coil winding magnetic flux of alternating magnetic field descends and impels self electric current to increase.Sheet metal is the closer to the coil winding of alternating magnetic field, and the coil winding electric current of alternating magnetic field is big more, and the eddy current that produces on sheet metal is also big.

As shown in Figure 1, the coil winding of alternating magnetic field is the coil of a LC higher-order of oscillation exciting curent, when the coil of sheet metal LC higher-order of oscillation exciting curent, produce eddy current in the metal sheet surface thin layer, because kelvin effect, in the thin layer of metal surface, produce eddy current I2, I2 produces alternating electromagnetic field again, reacts on the coil, makes and produces induced potential in the coil, cause the variation of coil equiva lent impedance Z thus, thereby also cause the variation of oscillating voltage amplitude.The amplitude of coil voltage detects easily, just can measure certain parameter according to the size of voltage magnitude.

The magnetic field that eddy current produces is analyzed the available equivalents circuit that influences of coil impedance, as shown in Figure 2.If coil resistance is R1, inductance is L1, and L2 represents the inductive effect that sheet metal presents eddy current, and R2 represents the eddy current loss resistance on the sheet metal, and coefficient of mutual inductance M represents the interaction degree between L2 and the L1, and M and distance X are inversely proportional to, and V is a driving voltage.Then have according to Kirchhoff's law

$R_1{\stackrel{\·}{I}}_1+\mathrm{j\ω}{L}_1{\stackrel{\·}{I}}_1-\mathrm{j\ωM}{\stackrel{\·}{I}}_2=\stackrel{\·}{V}$

$-\mathrm{j\ωM}{\stackrel{\·}{I}}_2+R_2{\stackrel{\·}{I}}_2+\mathrm{j\ω}{L}_2{\stackrel{\·}{I}}_2=0$

Can derive coil thus is subjected to the equiva lent impedance behind the vortes interference to be

$Z=[R_1+\frac{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="Y2008201575210011H1.png"\; state="\{\{state\}\}">R</figure-callout>}}_2{\mathrm{\&omega;}}^2{M}^2}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="Y2008201575210011H1.png"\; state="\{\{state\}\}">R</figure-callout>}}_2^2+{\mathrm{\&omega;}}^2{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="Y2008201575210011H1.png"\; state="\{\{state\}\}">L</figure-callout>}}_2^2}]+\mathrm{j\&omega;}[L_1-\frac{{\mathrm{\&omega;}}^2{M}^2{L}_2}{{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="Y2008201575210011H1.png"\; state="\{\{state\}\}">R</figure-callout>}}_2^2+{\mathrm{\&omega;}}^2{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="Y2008201575210011H1.png"\; state="\{\{state\}\}">L</figure-callout>}}_2^2}]=R+\mathrm{j\&omega;L}$

When ω is higher,

ωL ₂＞＞R ₂

Then have

$R\&ap;R_1+R_2\frac{L_1}{L_2}{\mathrm{<figure-callout\; id="2"\; label="K"\; filenames="Y2008201575210011H1.png"\; state="\{\{state\}\}">K</figure-callout>}}^2$

L≈L ₁(1-K ²)

Quality factor q is

$Q=\frac{\mathrm{\&omega;L}}{R}=Q_0(1-K^2)/(1+\frac{R_2{L}_1}{R_1{L}_2}{K}^2)$

$K=M/\sqrt{L_1{\mathrm{<figure-callout\; id="2"\; label="L"\; filenames="Y2008201575210011H1.png"\; state="\{\{state\}\}">L</figure-callout>}}_2}$

In the formula: K is a coupling coefficient; Q ₀=ω L1/R1 is the Q value of the coil of higher-order of oscillation exciting curent under the no vortes interference.This shows, under the certain condition of R1, R2, L1, L2, the mould of the equiva lent impedance of coil and quality factor are only relevant with coupling coefficient K, the size of K value depends on the distance X between coil and the sheet metal, under the I1 certain condition, the amplitude of excitation voltage just has definite relation with distance X, so just can measure coil voltage and measure distance X.Based on principle, stable extremely important to the I1 of the coil of higher-order of oscillation exciting curent, exciting curent must be very good constant current source, and the fluctuation of external voltage is quite little to the influence of I1, and distance X could only may be stablized.If the production of mass more needs good consistance.

TPL355 integrated circuit (IC) chip inside has oscillator stage, rectification stage, thresholding comparative degree, driving stage, hysteresis controlled stage, time-delay connection and inner voltage stabilizing level.The utility model has utilized its oscillator stage and inner voltage stabilizing level, inner static current sinking 0.5mA, the wide 4.5-36VDC of operating voltage, its operating voltage is provided by the accurate voltage stabilizer of XTR115 integrated circuit, stability is very good, TPL355 integrated circuit 5 oscillation frequency: about 100MHz, frequency of operation is not less than 2KHz

As shown in Figure 3, vortex induction pops one's head in for this reason that IC1 is a TLP355 integrated circuit 5, and FERRITE CORE and coil and oscillating capacitance are formed, and coil L and higher-order of oscillation capacitor C 1 are connected on the 1st, the 7 pin of the integrated electricity of TPL355, and feedback resistance R1 is connected on the 2nd pin and negative pole.The 8th pin is that the return difference adjustment directly connects negative pole, and the 3rd pin is an integration C2 electric capacity, and output terminal is unsettled.The voltage that the accurate voltage stabilizer of the 8th pin of power supply termination XTR115 integrated circuit 6 provides.Back circuit oscillates powers on, the inductance L two ends are measured as sine wave, and amplitude diminishes when metallic object is close, and TLP355 integrated circuit 5 belongs to the non-failure of oscillation type of amplitude change types special circuit, add that feedback resistance has only used 10%, therefore sinusoidal wave amplitude becomes the funtcional relationship of substantially linear with the metallic object displacement.The voltage doubling rectifing circuit that sine wave signal is formed by C3, D1, D2, C4, R2, its amplitude of variation becomes DC simulation voltage.The voltage of forming through the IC2 amplifier is penetrated a grade follow circuit again.

As shown in Figure 4, penetrate the output voltage V o of grade follower and the measured result of distance X, when setting the dynamic data deviation of demarcating, can finely tune feedback resistance R1 linearity only may be consistent.According to a large amount of data results of test repeatedly, this linearity repeatability is very consistent.The distortion of high-end and the low side linearity, technical requirement according to inductance core, the reliable detection distance is at below 60% of core diameter, non-cpntact measurement need be reserved certain non-contacting free mechanical trip at lower position, therefore getting high-end and the linearity low side interlude is that the dynamic range data are more satisfactory, the value of Xo, multiple to linear process or the dynamic expansion mode of Xo in actual applications, microprocessor is built list processing (LISP), because linear consistance height, be well suited for this kind mode and handle, mechanical aspects, tangent fan-shaped metallic object, metal eccentric wheel; The main dynamic expansion that embodies the angle aspect.

As shown in Figure 3, the IC3 quiescent dissipation that to be TLP355 integrated circuit 5 penetrate grade follower 7 with IC2 voltage is very little, DC simulation voltage linear lower limit is also low, and XTR115 conversion back minimum voltage can not guarantee to reach 4mA, just need use the measure of current boost to whole loop.The 1st pin of XTR115 integrated circuit 6 or the 8th pin to the 3rd pin resistance in parallel, are adjusted and made output equal 4mA, and this measure does not influence conversion; Only list the 1st pin the 3rd pin resistance in parallel among the figure three.

According to concrete range, determine that the maximum position between metallic object and the probe is upper limit displacement, adjusting W shunt makes and is output as 20mA.Determine that the minimum position between metallic object and the probe is the lower limit displacement, adjusting R2 is 4mA.

As shown in Figure 5, according to the formula to calculating of electromagnetic induction principle, the mould of the equiva lent impedance of coil and quality factor are very crucial, therefore requirement when coiling, and the automatic winding displacement coiling just can meet the demands.Described jar type magnetic core 1, its mass production require magnetic flux unanimity of will trying one's best, and the skeleton 2 of coil is the amboceptor of coil winding, general plastic injection piece, but requiring indeformable workpiece, the coil rack 3 that coiling is good is in the tank filling type magnetic core 4.

As shown in Figure 6, described thin metal layer 8, whole circle is wrapped magnetic core, welds an electric capacity then and is connected with power cathode, and 9 is sensitive surface, and the housing of the plastic casing 10 of probe is a column type or square, the right cylinder of listing among the figure; The plastic casing 10 that sensitive surface is packed probe down into adds charging into epoxy resin 11 then.

Change the probe size of coil with the composition of magnetic core of LC according to technical scheme, the voltage magnitude at the distance change coil two ends of the probe of the coil among metallic object and the LC and the composition of magnetic core and apart from proportional variation.Therefore the diameter of the probe of magnetic core and coil composition changes the size of magnetic core and coil as required in the 5-100mm scope.

As shown in Figure 3, described CZ is a magnetic bead, can filter high-frequency signal, and TVS suppresses the impact of the high impulse electric current of moment to circuit.

Claims (4)

1, two-wire system current mode displacement transducer constitutes the vortex induction probe by TLP355 integrated circuit and inductance core, voltage doubling rectifing circuit, voltage is penetrated a grade follower, shunt, XTR115 voltage/current conversion special IC, anti-jamming circuit is formed, it is characterized in that: the accurate voltage stabilizer voltage of described XTR115 voltage/current conversion special IC is supplied with the TLP355 integrated circuit, TLP355 integrated circuit and inductance core constitute the vortex induction probe, extract oscillator signal at the inductance two ends and carry out voltage multiplying rectifier, amplifier is penetrated level and is followed the back shunting to XTR115 voltage/current conversion special IC, the electric current 4-20mA that converts to output.

2, two-wire system current mode displacement transducer according to claim 1, it is characterized in that: the diameter size of described inductance core is in the 5-100mm scope.

3, according to the described two-wire system current mode of claim 1 displacement transducer, it is characterized in that: the periphery of described magnetic core, non-sensitive surface coated metal thin layer, and weld an electric capacity and link to each other with power cathode.

4, two-wire system current mode displacement transducer according to claim 1 is put, and it is characterized by: connect in the described XTR115 voltage/current conversion special IC input electric power loop magnetic bead, TVS in parallel pipe.

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